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MikeStephani

loss of power cont...the mystery turns....

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MikeStephani
Well, I and many of your were sure that it was points or condenser (PowerMax 20 hp Onan) but after today, I am convinced that it cannnot be electrical. Started today, had to mow about an acre of tall grass...ran great for 15 minutes (again) then started to sputter and lose power (it recovers at an idle). This time, however, I tried to stick with it by choking it and guess what?? It recovered. Now, this engine was rebuilt last August by a dealer so I know that it is supposed to be tight. I managed to choke it through the rest of the mow at about 40% power (I am guessing as it barely had enough power to mow) but I got the job finished. This tractor really gutted it out! The basic operation is to run the throttle at about 80 - 85% full and play with the choke at almost a complete choke to letting it off a little. I know that this sounds really bad, but with company coming for the holiday weekened and wife who has dubiously played along with my tractor obsession watching me and shaking her head all day...well, you get the picture. Does this sound like a fuel pump problem? Or is it something as simple as getting the carb cleaned and adjusted by somebody who knows more than I do? Fuel filter is new and still looks OK. I have taken the return-to-tank line off and cranked it too, it pumped OK from what I could see. Tractor warms up, then loses power and won't run at high RPM's....what is it? I don't know. I do know this (this ones for you JP) IT AINT FOR SALE ANY MORE. I really just became attached to it today and can see the potential of this machine. I gotta tell you, my hillbilly yard looks like it has been transformed into a pro-ball stadium field, and it has never looked this good. I've got some steep hills, and this thing (despite it's lack of power) never flinched. But, that does remind me, whenever I got on a hill, at any angle (except heading uphill) going down or across the sidehill, it would die again no matter how much I choked it. Contributing factor?? I don't know... the mystery deepens. If any of you "PowerMax Savants" know what is going on, please let me know. I'm not Mr. Goodwrench, but I'm not Stevie Wonder with a wrench, either.8) Thanks! - Mike

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jlasater
If it has a knob on the bottom of the carb, try screwing it in by hand and then back it out 1 1/2 turn as a start. If it still starts dying after that, I doubt it's a carb adjustment. I fixed someones freshly overhauled PowerMax back when I was a kid in high schooly just by doing that :-) He repaid me by letting me mow over an acre with the tractor, I was in heaven :-) You might try the $0.25 carb rebuild where you run it up to a decent engine speed and then stuff a rag over the carb intake which generates a serious vaccum. Occasionally that will dislodge junk in the fuel circuits. Just be sure the rag is folded up well so it doesn't suck into the carb :-)

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blackfarms1
I have a 9020 that does the exact same thing have gone through the electrical steps same as you. Hope someone can figure this thing out. Have noticed that return line to fuel tanks is always full of bubbles, is this normal? Thanks Sean

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firefoxz1
I would rerun new fuel lines away from any heat source and replace the gas cap and make sure all the heat shields and tin are on and maybe (if you haven't) clean out the gas tank. From what Sean said his sounds like vapor lock and that could be your problem also. I have slid 1/2"or5/8" hose over the fuel lines on a few tractor to help insulate them ( you could also just try the slit plastic covering they usually use for wires). If you can't keep the fuel line from laying on the engine try cutting a piece of wire coat hanger and taping it to the hose so it can be bent to hold the hose away from any contact (my way to replace preformed hose on cars sometimes). It could be dirt getting into a fuel curcuit in the carb but if it happens at the about the same amount of run time each time I would doubt that very much. I hope this was helpful and you understand what I am trying to explain.

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Marty-MN
If the engine accelerates from about 500 rpm to full throttle and back to idle without hesitation or dieing the carb adj should be close. I hate trying to turn the get at the main adj down under behind the fuel pump but if it doesn’t respond or in question try opening the main adj 1/2 turn at a time. I've used jlasater's rev it up and cover the carb with some success. :) Onan's check for the fuel pump is disconnect the line from the carb and place it in a cup, turn it over by hand and if fuel comes out it's ok. That did not cover low capacity due to a weak spring. A bad pump leaking gas into the crankcase can kill the engine :( good reason to put on an elect pump and shout off valve like D-17 Dave has posted in the past and the main carb adj is easier to get at. Firefoxz1 has a good point also, easy to try and low cost.:)

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MPH
Possible it's the wrong fuel filter, when I got my 4040 going several years ago I had put this new nice compact little ceramic filter on it. Acted just like your talking. Replace it with a regular bulky ugly paper element 1/4 inch line NAPA bought filter and problem went away. I have an electric pump on mine.

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Al
Hi, Try taking the hood off and mowing with it. These engine run very hot in these units. This may give you a clue regarding vapor lock problems. Are you using fuel with alcohol in it? Do you have any exhaust leaks? Put a piece of clear fuel line between the fuel pump and the carb and see if there any air bubbles in the fuel to the carb. Sounds like fuel vapor lock problems to me. These engine have adjustable main jets that are more prone to vapor lock problems than fixed jets. Back in the 80s when gas reformulations began in earnest vapor lock became a serious problem. What was happening was tiny air bubbles would lodge between the adjustment needle and the inside of the jet. These bubbles would collect and "block off" the jet, the engine would die sit for a couple of minutes the bubbles would break and the engine would restart and run fine for a while and then repeat the cycle when it was hot out. Manufacturers discovered that using a fixed jet even though the inside diameter was smaller than the jet used with a needle, the diameter was larger than the distance form the jet to the needle on the adjustable jets. Thus larger bubbles would slide through the fixed jet without sticking and vapor lock was significantly reduced. This was the major reason for the switch to fixed main jet carbs. EPA issues were further behind this. Needle stop caps were acceptable to the EPA. We just had a Case in last week with the same symptoms on a Kohler K341. The problem was the exhaust gasket was burned out on the carb side and exhaust was blowing on the carb. Putting a new exhaust gasket in the engine fixed it. Look for heat getting to the carb somehow. Al Eden

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blackfarms1
Thanks Al, that may very well be the problem. Both my pow'r max's are missing the heat shields that go on top of the motor. Any idea where I could find these? Is the what makes tha sides of the hood rust? Thanks, Sean

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babablacksheep
Bubbles in the return line to the tank are never normal. They indicate a pinhole leak in your fuel system. The engine probably runs fine at idle and when you first run it up, but as you maintain speed it begins to pull air into the system and leans the mixture out. The leaks are usually too small to drip fuel and only pull air under high throttle. Install a clear piece of fuel hose as the return line, start it up and watch it as you run it up to full throttle. It may take ten to fifteen minutes, but if you start to see bubbles in the clear line, replace the main fuel line and check all fittings for tightness.

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MikeStephani
THANKS FOR ALL YOUR HELP, YOU FELLAS ARE AWESOME! I FOUND THAT WHEN THE MECHANICS REBUILT ME ENGINE, THEY NEVER PUT HOSE CLAMPS ON THE FUEL LINE COMING OUT OF MY TANK. I PUT A CLAMP ON AND IT HELPED OUT A LITTLE; THEN I PUT A CLEAR PVC LINE ON MY RETURN. TRACTOR RAN GREAT UNTIL IT GOT HOT AND WHEN I REVVED THE THROTTLE, THE GAS IN THE RETURN LINE STARETED LOOKING LIKE A MILKSHAKE (LOTSA AIR). TONITE I WILL GET ALL NEW FUEL LINES AND START THE LOOKING FOR ALL MY LEAKS! THANKS AGAIN MIKE

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Simplicity314
Mike, don't run your tractor without the shields. They are not heat shields. They channel the air from the fan to go around your fins and keep the engine cool. I bet your valves are getting too hot. Don't run the tractor again until you find some.

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blackfarms1
Thanks for all the help guys. All engine covers are intact on both engines. However I have seen in some of the pics on this site a sheild on the top of the engine between the carb and the exhaust manifolds. Most of the pow'r max's do not have these. Are these needed? Where could I find or make these? Also is this what flakes all the paint off of the hood? When I repaint I would like to stop this somehow, thanks Sean

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Simplicity314
As for the paint, there's probably a new coat over old paint. Strip the entire hood down to metal, use etching primer and paint when there is low humidity. As for the shield between the exhaust and carb, they're good to have if you use a snow blower and the carb ices up or if you're experiencing vapor lock in hot weather. As for the shield, someone made one and posted pics, I think in Show and Tell..when I finish some more work I'll look for the link for you.

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MikeStephani
I have changed all of the fuel lines and done the 25 cent carb clean and it helped alot; however, I still am losing power. I noticed that my fuel filter (just changed it) goes from 2/3's full to only 1/5th of the way full when I am experiencing loss of power....does anyone think this could be a fuel pump issue? It comes and goes, but whenever it comes, the fuel filter seems to start running dry (almost - not all the way). Or this normal??? Thanks for your help! Mike

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StanD
Here is my suggestion: Take a clean plastic 2 gallon fuel container & strap it to the running board. Run a pickup hose to the bottom & a return hose just into the can. Put it thru a workout & see if this corrects your problem. The pickup tube in the original tank goes to within 1/8 inch of the bottom and the smallest flake of rust will restrict the flow. Nearly all the Powermaxes I have owned have had bad fuel caps/plastic cracked or totally broke out therefore allowing water into the tank. I just removed the pickup tube from a rusty tank that I had that I had that very same problem with. At the time I just replaced it with a clean tank but your post made me go out and remove the tube to check it out. Guess now I will have to put some course chicken grit in the tank & try the strap it to a wheel trick to loosen all the rust, cream the tank, & solder in a new pickup tube. Give the known clean fuel container a try & see how it goes. By the way it seems the AC,s don,t have as much of a problem because the cap is under the hood. Seems you have tried everything else so I suggest you give this a try. StanD

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Guest
Attn: blackfarms1 After you get the heatsheilds installed, install a fan in the grille as I did. [img]/club2/attach/mikefox/Fan.jpg[/img] Fan blowing out.

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blackfarms1
thanks for all the great help guys. as it turns out the only thing wrong with the 9020 was the carb was out of adjustment. one of the earlier posters suggested this but I thought it was too simple. tractor would run fine till warm or when it got a load on it. if you caught it soon enough you could reduce to idle and it would recover. opened up jet 1/2 turn runs like a top thanks sean

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BigSix
Mike: If you can only get the engine to make enough power to mow, by using almost full choke, that tells me you're having fuel starvation, for any of the number of possible reasons discussed already. Here's the thing: because it needs so much choke, that's almost certain to mean you're running way too lean. Counterintuitively, when you run lean (with too little gas, as opposed to rich, with too much gas) you're more likely to overheat the engine. You would think more gas would make it run hotter, but that's not the case. The incoming charge of gas actually cools the engine significantly. With less than the proper fuel-to-air ratio, the engine will run hotter than normal. What I'm trying to say is, running lean and forcing the engine to work under those consditions risks serious engine damage, IMO. This is a bigger problem with two-stroke snowmobiles, where a too lean mixture can easily result in a seized engine. But even though it's a four-stroke, if it were my machine, I would not put it under load until I was assured that the mixture was adequate. Hopefully the clear gas lines will solve the mystery. If not, I'd seek someone with some deeper carb and fuel pump experience. Best of luck.

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